This invention relates generally to grapples and hoists and more particularly to grapples used to seize, lift, transport, lower, and install the various internal components of nuclear reactors, especially nuclear fuel assemblies.
The component to be moved is usually located in a hostile environment such as hot water or liquid sodium and may be radioactive or located in a radiation field. The operator is usually some distance from the site of the task, and often cannot see the component and grapple. Despite this and other handicaps, the grappling task requires accuracy and care due to close tolerances and safety considerations. An expeditious, speedy performance of the grappling task can reduce plant downtime and personnel radiation exposure.
The grapples presently in use employ a variety of electrical and mechanical devices to monitor the grapple location and status, and control grapple operation. Verification of proper seating of the grapple is often accomplished visually, followed by operator-initiated grapple seizure. When visibility is hampered or impossible, the operator may rely on time-consuming trial-and-error operation.
Accordingly, it is desired to provide a grapple which is safe and reliable and which operates automatically without the operator's visual verification of proper seating.